The present invention relates to hydrokinetic coupling apparatus for a motor vehicle.
The present invention relates more particularly to hydrokinetic coupling apparatus of the type which is described in the document FR-A-2 748 539. In that document the apparatus includes an input element in the form of a casing having a generally transversely oriented wall and an output element comprising a turbine wheel assembled with a hub, which are together mounted inside the casing. A piston is located between this assembly and the transverse wall. The piston is mounted for axial movement with respect to the transverse wall and it is coupled in rotation to the latter.
The input element is arranged to be coupled in rotation through its transverse wall to a driving shaft, while the output element is arranged to be coupled in rotation to a driven shaft through its hub.
The piston has at its outer periphery a surface called the second surface, while the transverse wall has a first surface facing the second surface. The surfaces in this case are friction surfaces, with one or more friction discs being interposed between the two surfaces.
By varying the pressure on either side of the piston, the latter is displaced axially in one direction or the other. The piston is accordingly movable axially with respect to the hub.
In the said document, the friction disc is provided at its outer periphery with lugs which extend outside the piston so as to mesh with an input member of a torsion damper, which includes an output member having a damper plate coupled to the hub. Circumferentially acting elastic members act between the input and output members, which are so configured as to receive the elastic members, which lie radially outside the piston and the surfaces.
It can be desirable to increase the external diameter of the surfaces, which is not possible having regard to the presence of the elastic members.
Accordingly, an object of the present invention is to increase the outside diameter of the surfaces, and to do so in an inexpensive way.
According to the invention, hydrokinetic coupling apparatus, especially for a motor vehicle, of the type which comprises a casing having an annular axial wall and a transverse front wall, of the type in which the casing is arranged to be coupled in rotation to a driving shaft, of the type that includes a turbine wheel mounted inside the casing and fixed to a hub which is arranged to be coupled in rotation to a driven shaft, of the type in which the rear face of the transverse front wall of the casing includes a first surface, of the type in which a lock-up clutch is interposed operatively between the turbine wheel and the transverse front wall so as to couple them together releasably, and of the type in which the lock-up clutch comprises at the rear a piston which is movable axially with respect to the transverse front wall of the casing, and which carries on its front face a second surface facing the first surface, is characterised in that the piston is coupled in rotation to the annular axial wall of the casing through an axially elastic device.
Thanks to the invention it is possible to increase the outside diameter of the surfaces, because there is no longer any restriction due to the presence at the outer periphery of the transverse wall of the casing of a damping device or a device for coupling the piston to the casing.
According to further features of the invention:
the second surface is situated in the vicinity of the outer periphery of the piston;
the axially elastic device comprises at least one support member coupled in rotation and axially to the axial annular wall of the casing and comprising a transverse plate element, and comprises at least one elastic member which is interposed axially between the piston and the transverse plate portion of the support member, and the piston includes means for coupling it in rotation with the support member;
the mean radius of intervention of the elastic member is smaller than the external radius of the second surface;
the axially elastic device comprises a plurality of support members spaced apart circumferentially, in particular at regular intervals;
the axially elastic device comprises a single support member, the transverse plate portion of which constitutes an annular ring;
the piston includes at its outer periphery an axial skirt which extends towards the rear and includes notches, and the transverse plate portion or portions of the support member or of the respective support member, constitute annular ring sectors, such that the annular ring sectors are received in the notches of the axial skirt of the piston, whereby to enable the support members to come into abutment against the edges of the notches in the piston;
the transverse plate portion of the support member has notches, and the piston includes pads on its rear face facing the said notches, whereby the pads of the piston are received in the notches of the transverse plate portion so as to couple the piston in rotation with the support member;
the coupling in rotation between the piston and the support member or members includes a circumferential clearance;
the axially elastic device comprises axially elastic tongues, the opposed ends of which are secured respectively on the piston and on the transverse plate portion of the support member or members;
the tongues exert a preloading force on the piston in the direction of locking of the clutch;
the magnitude of the preloading force is adjusted according to the axial positioning of the transverse plate portion;
the tongues tend to retain the piston in the unlocked position of the clutch;
the tongues are spaced apart circumferentially at regular intervals;
the tongues are oriented tangentially;
each tongue includes a first point for fastening on the rear face of the piston;
the first fastening point is defined on a convex boss on the rear face of the piston;
the tongues are formed integrally with the transverse plate portion or portions of the or the respective support member;
each tongue has a second point for fastening on the front face of the transverse plate portion or portions of the or the respective support member;
the second fastening point of the tongue is in facing relationship with a concave boss on the rear face of the piston;
the transverse plate portion of the support member is formed with cut-outs in facing relationship with a first fastening point of each tongue, the second fastening point of which is situated in the vicinity of the circumferential terminal edge of the cut-out;
the axially elastic device comprises at least one compression spring in axial engagement, firstly on the rear face of the piston and secondly on the front face of the transverse plate portion or portions of the or the respective support member, whereby the spring exerts a preloading force on the piston in the direction of locking of the clutch;
the axially elastic device comprises a single annular spring of the helical type or of the conical type or of the corrugated type;
the axially elastic device comprises a plurality of compression springs which are spaced apart circumferentially at regular intervals;
each compression spring is of the helical type, and at least one end of each spring is hooked on a retaining pad formed in projecting relationship on the front face of the transverse plate portion or portions of the or the respective support member and/or on the rear face of the piston;
each compression spring is a spring sector of the conical ring type or corrugated type;
the transverse plate portion or portions of the or the respective support member include at their inner periphery an axial skirt which extends forward so as to retain the springs radially inwards;
the transverse plate portion or portions of the or the respective support member includes pairs of circumferentially opposed abutments, which extend axially forwards to retain the spring sectors circumferentially;
each spring sector of the corrugated type is fixed through its circumferential ends on the transverse plate member or members of the or the respective support members;
the axial annular wall of the casing includes transverse lugs which extend towards the axis and each of which has a notch, and the support member includes on its outer periphery transverse lugs, each of which has on its rear face a projecting boss facing a recess, whereby the support member is coupled in rotation with the axial wall of the casing by a bayonet type coupling;
the piston includes, in facing relationship with its rear face, at least one transverse intermediate plate which is fixed through its outer periphery on a peripheral annular skirt of the piston, whereby the elastic member is operatively interposed between each transverse intermediate plate and each support member;
the casing comprises a front shell and a rear shell, each of which includes an axial skirt, the two axial skirts defining the axial annular wall of the casing;
the transverse plate portion of each support member is fixed directly on the free rear end of the axial skirt of the front shell, or on the free front end of the axial skirt of the rear shell;
each support member comprises an annular axial crown or annular axial crown sectors, which are oriented towards the rear from the outer periphery of the transverse plate portion, for coupling the support member to the axial annular wall of the casing;
the crown or the crown sector of each support member is fixed on the axial skirt of the front shell or on the axial skirt of the rear shell;
the crown or the crown sector of each support member is fixed between the axial skirt of the front shell and the axial skirt of the rear shell;
a double-sided annular friction disc is arranged to be gripped between the first and second surfaces, and a torsion damper is interposed operatively between the annular friction disc and the hub of the turbine.